I believe you're confusing terms. If you've only lived for 4 years in the UK you don't have permanent resident (PR) status yet.
Only after living for 5 years in the UK you can get PR status (if you meet the PR conditions), and you need to apply for a card (DCPR) to confirm that status. And you can only apply for British Citizenship after you held the PR status for 1 full year. You also need the DCPR to apply for citizenship.
If you leave the UK now and stay abroad for 6+ months, you will lose the PR continuity and you cannot get the DCPR, and your PR clock resets to 0.
I'm not a solicitor so take this with a grain of salt
PS. If I were you I would forget about that 6-month contract - if you really want the British Citizenship. Find another contract in the UK. After you get your British cit & passport you can go work wherever you want for as long as you want.